The invention relates to an energy absorption structure for a vehicle, having an absorption of energy element and at least one impact transmission element, which impact transmission element is pressed against a side wall of the absorption of energy element and, in the event of an impact, can be guided along the side wall.
Impact or crash structures made of carbon-fiber-reinforced plastic (“CFRP”) are currently predominantly used in vehicles as carriers with a rectangular or round profile cross section. In the event of an impact, the failure mechanism of what is referred to as crushing is applied to absorb energy. In the event of crushing, complete disintegration (pulverization) of the carrier takes place predominantly through brittle fracturing, to be precise successively at an end-side “crash front” which penetrates further and further into the carrier as the impact progresses. A further form of destruction of the impact structure is the defined deflection of the CFRP material through 180° directly at the crash front (“fronting”). In this context, the fiber fracturing mechanism in conjunction with friction comes into effect in order to dissipate the kinetic energy.
In the event of a head-on impact, the two failure mechanisms function in the longitudinal direction of the carrier in which the force is perpendicular to the carrier cross section. However, under the influence of transverse forces, structures which are configured for these failure mechanisms fail in a largely uncontrolled and catastrophic fashion unless costly additional structural measures are provided to absorb the transverse forces. Analytic treatment of the failure modes is currently not possible. In addition, an unfavorable dependence of the CFRP material on temperature becomes apparent, since the absorbed energy generally decreases at relatively high temperatures.
DE 10 2010 020 080 A1 discloses a bumper arrangement for a motor vehicle, which bumper arrangement has a transverse carrier and a crashbox, wherein the transverse carrier is coupled via a guide profile to the crashbox and the guide profile is connected in a relatively movable fashion to the crashbox, wherein a clip for coupling to the crashbox is provided on the guide profile. However, this does not bring about any increased absorption of energy.
DE 10 2004 059 545 A1 discloses a device for absorbing energy, in particular in the event of a collision of a vehicle with a solid body. The absorption of energy device comprises a movable shock impact transmission element and a locking device for influencing the mobility of the shock impact transmission element. The shock impact transmission element can be locked rigidly in a first, minimum impact speed region by means of the locking device, whereas in a second, high impact speed range the shock impact transmission element can move in an essentially force-free fashion. The absorption of energy device is distinguished by the fact that the locking device also permits the relative movement of the shock impact transmission element within the entire movement stroke in a third, central impact speed range. In this context, the absorption of energy device comprises a shaping arrangement which can be controlled by the locking device as a function of the crash, for the defined plastic deformation of material, wherein the shaping arrangement can be driven by the relative movement of the shock impact transmission element. However, this shaping arrangement is suitable only for deforming metallic material and not for non-ductile fiber composite materials.
The object of the present invention is to overcome the disadvantages of the prior art, at least partially, and in particular, to make available improved absorption of energy on fiber composite elements.
This object is achieved according to the features of the independent claims. Preferred embodiments can be found, in particular, in the dependent claims.
The object is achieved by an energy absorption structure for a vehicle comprising a first element, referred to below as “absorption of energy element”, and at least one second element, referred to below as “impact transmission element”. The impact transmission element is pressed against a side wall of the absorption of energy element and, in the event of an impact, can be guided or displaced along the side wall. In other words, in the event of an impact or crash, the impact transmission element is guided along the side wall, or pulled or pushed over the side wall, at least for a certain distance.
The absorption of energy element is a fiber composite component, with the result that absorption of energy is not brought about by its plastic deformation. Instead, the impact transmission element has a microstructure which can be or is countersunk into the absorption of energy element or into the fiber composite component. As a result, positive locking with the absorption of energy element is achieved, with the result that in the event of an impact the microstructure “ploughs”, scratches or claws superficially, in accordance with its penetration depth, through the absorption of energy element. As a result, the side wall is superficially destroyed in the path of the absorption of energy element or of the microstructure. This superficial destruction gives rise to a high level of absorption of energy at the absorption of energy element, without destroying the absorption of energy element by the movement of the impact transmission element over the entire depth. As a result of the retention of the absorption of energy element as such, said element has a residual load-bearing capacity there, which permits the structural integrity to be maintained after an impact. In addition, the failure mode is independent of a force introduction angle, with the result that the carrier itself can be dimensioned for any desired transverse forces.
The degree of destruction of the surface, which correlates to the absorption of energy, can be influenced, in particular, by the penetration depth or pressing in depth of the microstructure, the pressing force during the impact or the displacing and by the shape and arrangement of the microstructure. In particular, in this way, a common property is made possible for different vehicle variants. The scaling of the absorption of energy and of the associated force level can consequently be carried out with a constant component geometry (for example with respect to a profile cross section and wall thickness).
The fact that the microstructure can be countersunk includes the case in which the microstructure is countersunk in the absorption of energy element, that is to say, in particular, is also already countersunk in the non-displaced state (state of rest). The fact that the microstructure can be countersunk also includes the other case in which in the state of rest the microstructure is not yet countersunk in the absorption of energy element, or only is so to a slight degree, but is countersunk or pressed in with a displacement relative to the absorption of energy element.
The energy absorption structure may be, for example, an impact structure or crash structure of the vehicle, for example a front-side or rear-side crash structure.
The vehicle may be, in particular, a motor vehicle, in particular a passenger motor vehicle.
The absorption of energy element may be, in particular, an engine longitudinal carrier (“MLC”).
The absorption of energy element may, as a fiber composite component, have glass-fiber-reinforced plastic, referred to for short as GFRP, carbon-fiber-reinforced plastic, also referred to as CFRP, or aramide as the fiber composite material.
The microstructure may be distinguished, in particular, by the fact that the individual structural elements (for example individual teeth) have size values in the micrometer range, that is to say do not exceed one millimeter. Therefore, in particular a penetration depth may be limited to a value of one millimeter or less. This is substantially less than a wall thickness of an associated side wall of typically at least three millimeters or more. The comparatively small height of the microstructure prevents complete destruction of the side wall over its entire depth in the path of the microstructure. However, the microstructure is not limited thereto. For example, a penetration depth may also measure more than one millimeter, for example if a thickness of the absorption of energy element measures more than three millimeters. It is a development that a height or a penetration depth of the microstructure is not more than a third of a thickness of the absorption of energy element below the microstructure, preferably not more than a quarter of the thickness. In this way it can also be achieved that the absorption of energy element is only superficially destroyed.
The fact that the impact transmission element can be guided along the side wall in the event of an impact means, drawing the reverse conclusion, that in a state of rest or normal state without an impact or in the event of an impact with such a low level of energy that the impact transmission element is not (relatively) displaced, the impact transmission element remains in a normal position or position of rest on the absorption of energy element.
So that the microstructure does not experience wear or self-destruction during its displacement, it is advantageous for it to have a greater degree of hardness and/or greater strength than the fiber composite material.
It is a development that the impact transmission element has a microstructure composed of metal and/or ceramic. In particular, the impact transmission element may be composed of metal, for example of steel.
Bending of the absorption of energy element during the guiding or displacement of the impact transmission element could lead to nonuniform destruction of the surface thereof. It is therefore preferred for the absorption of energy element to be a virtually rigid and stiff element.
It is a development that the impact transmission element can be guided, in the event of an impact, along the side wall by a crashbox, a deformation box (“defobox”) or a bumper. The impact transmission element may alternatively constitute part of these functional elements.
It is a refinement that in a normal state or state of rest (without an impact or with only a slight impact) the impact transmission element is micro-serrated to the absorption of energy element in a positively locking fashion. As a result, absorption of energy or energy dissipation is already achieved immediately at the start of a relative displacement of these two elements. Micro-serration can be understood to mean, in particular, that the countersunk microstructure and the corresponding region of the absorption of energy element are shaped in such a way that they engage in each other without play. In particular, the two elements may have a complementary shape in this case.
It is also a refinement that at least one impact transmission element is arranged on an outer side of the side wall of the absorption of energy element or fiber composite component. This permits particularly simple attachment and can be applied even in the case of a non-hollow or solid absorption of energy element.
It is a further refinement that at least one absorption of energy element is a hollow element, in particular a hollow profile, and the impact transmission element is arranged on an inner side of the side wall. This permits a particularly compact design.
It is also a further refinement that at least one deformation element has a microstructure with a field of cone-like (i.e. cone-shaped and/or frustrum-shaped) and/or pyramid-like (i.e. pyramid-shaped and/or truncated-pyramid-shaped) (micro) projections. These permit dissipation of energy, which dissipation is at least largely independent of a direction of displacement of the impact transmission element.
It is also a refinement that at least one impact transmission element has a microstructure with a field of elongated projections which are arranged parallel to one another. The elongated projections may have, for example, a triangular cross-sectional shape and have, for example, a hipped-roof-like basic shape. The elongated projections can also be considered to be fins. Such a microstructure has the advantage that, given orientation of the elongated projections in an envisaged direction of displacement, uniform dissipation of energy over the travel is assisted, for example by a reduction in a load peak or force peak at the start of the displacement process. In this refinement, removal of destroyed fiber composite material from the path of the impact transmission element is also assisted. As a result, the accumulation of material under the impact transmission element can be counteracted.
It is also a refinement that at least one impact transmission element has a microstructure with a field of V-shaped projections. This also brings about more uniform dissipation of energy, in particular if the V-shaped projections are oriented with their tip in a provided displacement direction. Removal of destroyed fiber composite material is also assisted here.
However, the shape of the microstructure is not limited thereto and may, for example, also have a field of irregularly arranged and/or irregularly shaped projections. The irregular microstructures may form, in particular, a rough surface with a defined roughness.
In addition, it is a refinement that the absorption of energy element is a profile element, that is to say an elongated element, which has an at least substantially identical cross-sectional shape at least over one section over which the impact transmission element is guided (“path”). In this context, slight deviations from the basic shape may occur locally, for example through the provision of holes or the like. The refinement as a profile element has the advantage that a displacement or a path of the impact transmission element can take place in a plane which is parallel to the longitudinal extent of the absorption of energy element, in particular linearly. Therefore, uniform displacement of the impact transmission element against the absorption of energy element is achieved again, and also uniform dissipation of energy.
The absorption of energy element may be, for example, an O-shaped, U-shaped or C-shaped profile element, in particular with a rectangular cross section.
However, the invention is not limited thereto, and the absorption of energy element may have, for example, a cross-sectional shape and/or size which changes over the length of the path of the impact transmission element. For example, the absorption of energy element may widen in the direction of the path of the impact transmission element and therefore, if appropriate, a contact pressure, therefore a degree of destruction and consequently absorption of energy of the absorption of energy element, can increase with an increasing length of the displacement.
It is also a refinement that a least one impact transmission element is plate-shaped. This has the advantage of easy manufacture. In particular, one side of the plate may be at least partially in contact with the absorption of energy element, and an associated contact face can have the microstructure. The microstructure may be arranged coherently or in a plurality of partial surfaces, spaced apart from one another, on the impact transmission element.
In addition, it is a refinement that at least one impact transmission element is attached to at least one side wall of the (then hollow) absorption of energy element by means of at least one screw or a rivet. As a result, in the normal state firstly the impact transmission element can be attached securely and precisely to the absorption of energy element. Secondly, in the event of an impact an even greater quantity of energy can therefore be transmitted to the absorption of energy element, since with the displacement of the impact transmission element the at least one screw or the one rivet is also pulled through the absorption of energy element. As a result, a continuous fracture line can be pulled through the absorption of energy element in the path of the screw or of the rivet, and/or a slit can be generated behind the screw or the rivet, for the generation of which energy is additionally required. The failure mechanism which is used is based on the bearing stress. In this context, strips of only superficially destroyed fiber composite material are present between the at least one fracture line, with the result that despite the high absorption of energy the absorption of energy element has residual strength or residual load-bearing capacity. The use of the at least one screw or of the one rivet has the further advantage that in this way a pressing force of the impact transmission element on the absorption of energy element can be adjusted. Particularly precise adjustment is provided when a screw is used.
In one development, the screw or the rivet may be guided only through that wall in the absorption of energy element to which the associated impact transmission element is attached. In another development, the screw or the rivet may be guided through two, in particular opposite, walls. In particular, an impact transmission element may be attached in each case to opposite walls of the (then hollow) absorption of energy element, in particular by means of at least one common screw. This permits particularly uniform absorption of energy on both sides as well as particularly simple mounting.
Instead of or in addition to the at least one screw and/or the at least one rivet, any other attachment element which connects the impact transmission element to the absorption of energy element in a positively locking fashion, and preferably also in a frictionally locking fashion, and which can generate fracture lines in the absorption of energy element, may also be used.
It is also a refinement that the plate-shaped impact transmission element is pre-curved before mounting, and in the mounted state is attached against its curvature to the absorption of energy element. In this way, a particularly high pressing force is generated, which particularly reliably ensures a sufficient insertion depth or penetration depth of the microstructure in the absorption of energy element even in the case of high displacement speeds of the impact transmission element. In particular, the impact transmission element may be pre-curved so as to protrude from the absorption of energy element.
It is also a further refinement that at least one impact transmission element is a bi-metal element which brings about a higher pressing force as the temperature increases. As a result, absorption of energy which is less when the temperature is relatively high can be at least partially compensated by fiber composite material.
In addition, it is a further refinement that at least one impact transmission element is a bi-metal element which makes available a larger surface of the countersunk microstructure as the temperature increases. It is therefore also achieved that absorption of energy which is less when the temperature is relatively high can be at least partially compensated by fiber composite material. The provision of the relatively large area of the microstructure can be implemented, for example, by virtue of the fact that the impact transmission element is a bi-metal element which is partially curved away from the absorption of energy element, and the curvature thereof reduces as the temperature increases. As a result, as the temperature increases a larger area of the microstructure bears on the absorption of energy element.
Basically, the energy absorption structure may have one or more absorption of energy elements which can each be assigned one or more impact transmission elements in turn.
In order to mount the impact transmission element on the absorption of energy element, it is preferred to countersink, in particular to press, the microstructure into the absorption of energy element. Subsequently, in particular after the implementation of a positively locking arrangement, the contact pressure can be reduced, if appropriate. The remaining (reduced) contact pressure is preferably dimensioned in such a way that the toothed arrangement during the (relative) displacement in the absorption of energy element remains and it does not become detached from the surface of the absorption of energy element.
In the following figures, the invention will be described in more schematically accurate detail on the basis of exemplary embodiments. In this context, for the sake of clarity identical or identically acting elements can be provided with the same reference symbols.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.